Method and apparatus for fabricating grid structures for cathode-ray tubes



Feb. 18, 1958 H. R. PATTERSON 2,324,251

METHOD AND APPARATUS FOR FABRICATING GRID STRUCTURES FOR QATHQDE-RAY TUBES Filed Jan. 14, 1953 2 Sheets-Sheet 1 Jigl ATM/MEX? Feb. 18, 1958 H. -R.- PATTERSON 2,824,251

' METHOD AND APPARATUS FOR FABRICATING GRID STRUCTURES FDR CATHODE-RAY TUBES 2 Sheets-Sheet 2 Filed Jan. 14. 1953 m J 5 1 H TIL N m n w w. W M 3 B a 9 7 W 7 w 6 .7 4 u a M u.. LIV. W 8 U MNIPXHEHIIIJII .l A If 5 a L7 9 H w x I um m w 7...u 9M W. W n u a w Uited METHOD AND APPARATUS FOR FABRICATING GRID STRUCTURES FOR CATHQDE-RAY TUBES Howard R. Patterson, Oakland, Calif., assignor to Chromatic Television Laboratories, Inc., New York, hf. Y, a corporation of California Application January 14, 1953, Serial No. 331,200

6 Claims. (Cl. 313-78) This invention relates to electron tubes and particularly to cathode-ray tubes of the variety wherein the so-called post acceleration deflection and focusing controls are introduced by way of a grid electrode arranged substantially adjacent to the final target surface upon which the electro-optical image effects are to be created.

Tubes of the so-called post acceleration type have al ready been disclosed in the art. One example of a tube of this character is found in the disclosure of the application for Letters Patent of the United States, Serial No. 265,366, filed by Ernest 0. Lawrence on January 8, 1952, now U. S. Patent No. 2,269,675, granted February 16, 1954. The present invention finds its principal utiliza tion in the construction of a grid electrode structure which may be used, for instance, in tubes of the type disclosed in the aforesaid application for Letters Patent, as above identified, or the invention herein to be set forth and described may find utilization in connection with other types of tubes of generally related purpose.

In a cathode-ray tube device wherein the electron beams from one or more sources, such as the usual electron gun, are arranged to be directed toward a final target area in the tube to produce electro-optical images as a result of tracing a raster on the phosphor coated target area, the scanning cathode-ray beam or beams (depending upon whether there is a single electron gun or a multiplicity of guns) is arranged to reach the phosphor coated target. of the tube through a final grid structure which is placed substantially adjacent to the screen or target. The grid so arranged comprises a multiplicty of tightly stretched parallelly arranged wires or conductors located in spaced relationship to each other by distances which are of the order of the dimension of one point of the image produced on the target. In some instances the spacing of the grid wires can be even less than image point dimension. The so stretched parallelly positioned grid wires cover an area transversely of the tube which is of generally the same order as that of the standard television raster to be traced. The phosphor coated target of the tube is customarily coated on that side which is faced toward the cathode-ray beam scanning source with an extremely thin metal film. A coating or film of this character is electron permeable and is so thin as to be readily penetrated by the impacting electron beam or cathode ray. The coating serves as a conductor to which relatively high voltages may be applied for accelerating the impacting cathode-ray beam. It also serves to reflect light from the impacted and electron-excited phosphor coating outwardly from the tube.

The combination of the grid and the coated target upon which voltages in the range of 1:3 may be applied then cooperatively function to provide both a post acceleration effect by which the impacting beam is accelerated toward the target in a region immediately adjacent to the target and also by reason of the relationship of the potentials applied to the screen and target film coating relative to each other, provide a multiplicity of adjacent 2,824,251 Patented Feb. 18, 1953 ly positioned electron lens elements by which the impacting cathode ray is sharply focused upon the target itself as it sweeps the target.

In some forms of the grid structure positioned adjacent to the target all wires of the grid are maintained at the same potential. In other forms of tube constructions alternate grid.- wires are connected together to form two ets of wires or conducting strands. Voltages applied to these two sets of wires may be of such order that'the wires may at times be of like potential relative to the target or one set of wires may be of higher (more positive potential) relative to the target than the other set, or vice versa, to provide the effects of deflection of the scanning beam just prior to its impacting the target. This deflection is completely supplementary to the normal but directional deflection introduced in the region of the electron gun to cause a tracing of the raster. Deflection introduced bythe'gridelement itself is adapted to cause a shift in the position of the impacting scanning beam over a position of a fraction only of one image point of the target.

It is important in the tracing of the raster on the tube target andparticularly so in connection with color television operations that a precise and accurate spaced relationship exist at all times between the individual wires of the grid and between the wires of the grid and the individual phosphorareas ofthe target. If this precisely established relationship is not maintained throughout it is substantially impossible to produce television images which are completely satisfactory as being shadow free and devoid of color contamination. This is because of the fact that the impacting scanning beam or beams will not impinge upon the desired area of the target (with misalined grid wires) to produce the intended color representation. In order that the point size of the image created on. the tube target shall be maintained constant throughout the complete target area of the image itris essential that the selected distance between the individual grid wires and the grid wires as a whole and the. phosphor target be precisely and rigidly maintained at all times.

Various approaches have been taken to provide grids for cathode-ray tubes which will meet these rigid requirements. Some considerable success has been. had in solving the problem by exercising great care in tube assembly and fabrication, but, generally speaking, it has heretofore involved great expenditures of time and exorbitant outlays of money for labor to provide the precision parts for each and every grid constructed. Operations of this nature, accordingly, make the grid itself and, therefore, the color tubes with which the grids are used, very expensive compared to cathode-ray tubes used to produce images in monochrome (e. g., black-andwhite). Further than this, great difliculties have been encountered in the building in such fashion and by ordinary methods of a practical grid capable of withstanding the high bake-out temperatures at which the cathode-ray tubes must be maintained in processing.

In practicing the present invention recourse is had to a proposed manufacturing procedure, apparatus and method by which a precision form of construction can be realized through relatively inexpensive manufacturing methods but which will nonetheless provide the required degree of accuracy and exactness in the final product and yet which will also withstand the heat of tube processing bake-outs. A tube construction of the type herein to be set forth is one by which the tube manufacturing costs can be reduced considerably by provisions of structure whereby the grid wires which are tightly stretched before and after bake-out are able to withstand the high heat incurred in the process and still not sag or become loose subsequent thereto. To this end, the relationship of the coefficients of linear expansion of the grid wires and the supporting frame are so established that with a rise in temperature the wires of the grid will expand more than the stretching or the supporting member of the frame. Consequently, the grid wires will not snap with frame expansion on heating during tube bake-out. With tube cooling, subsequent to baking, it will be evident that the grid-wire shrinkage will cause the wires to tighten to prevent possible sag, malpositioning and excessive vibration.

To achieve the objectives of this invention, the color control grid is formed of a different metal than the support structure, or it is of a different alloy of the same base metal. The color control grid is assembled by prespacing the required number of grid wires initially on a separate spacing fixture made to a high degree of precision. When the grid wires are so positioned and stretched tightly they are clamped or gripped in the selected location in proximity to the support frame and then secured in this chosen position to the frame. For tube constructions in which the wires are to be used for focusing action only all wires of the grid are connected together for operation as a unipotential structure. Where the grid is to be used in connection with the tube wherein deflection to achieve color control is to take place between the wires the grid wires are fastened so that adjacent wires are insulated one from the other. Various materials may be used for the formation of the grid and its support elements. To this end, recourse may be had to the known fact that the coefficient of linear expansion of ferrous alloys may be very rigidly controlled by the addition of nickel. When so arranged, according to this invention and in one form thereof, stainless steel components may be used with one form satisfactory for the grid wire or conductors and another form satisfactory for the support.

The precise method and procedure by which such a grid structure is fabricated is more fully set forth in the description to follow, from a reading of which it will be evident that among the objects of this invention will be those of providing an improved form of grid wire structure usable in connection with a cathode-ray tube wherein post acceleration and focusing is introduced in a region immediately adjacent to the tube target whereupon the image is developed, and to form a type of grid structure which may be so used with or without deflection in the region of the target.

A further object of the invention is that of providing a grid structure suitable for cathode ray tubes wherein precisional accuracy is obtainable according to methods which can reduce substantially the cost of construction by reason of the introduction of precision establishing equipment as a part of the manufacturing process rather than as a part of the tube construction itself.

Other objects of the invention are those of providing an improved form of focusing, accelerating and deflecting grid wire structure for a cathode-ray tube which will not be subject to a weakening or distortion during the bakeout procedure in the tube into which it is assembled for use.

Further objects are those of improving overall construction of the cathode ray tube, and particularly one of the variety adapted to produce color images, which shall be of a nature suitable to insure a final tube which is more efiicient, cheaper to construct and more rugged than those of the type including grid wire structures than have been heretofore built.

Still other and further objects and advantages of the invention will become apparent and at once suggest themselves to those skilled in the art to which thisis directed by continuing a reading of the description to follow in connection with the accompanying drawing and the claims hereto appended.

Considering the drawings:

Fig. 1 shows by schematic and diagrammatic representation, partly in section, apparatus by which the method and principles of this invention can be elfected;

Fig. 2 is a diagrammatic representation in plan of the device of Fig. 1, with one of the upper sections of the wire gripping member still in place;

Fig. 3 is a plan on a greatly magnified and exaggerated scale of a portion of the spacer bar for conductor positioning showing particularly the notched grid wire conductor locating portion with two such grid wires positioned in the slots or notches;

Fig. 4 is an end elevation of the spacer bar of Fig. 3, also greatly enlarged;

Fig. 5 is a schematic representation of one form of apparatus for removing conducting strands of wires from a storage spool or reel for location by the spacer bar arrangements of Figs. 2 through 4;

Fig. 6 is a schematic showing of a clamping element for use with a wire supporting structure of the form shown by the apparatus of Fig. 5;

Fig. 7 shows partly in section one form of the lower member of the clamp for holding the grid wires prior to utilization and positioning in the apparatus of Figs. 1 and 2;

Fig. 8 shows in section a portion of a schematic representation of a cathode-ray tube in which the grid structure is incorporated; and,

Fig. 9 is a section taken on the line 99 of Fig. 8 looking in the direction of the arrows.

Various ways and means for initially winding the grid structure may be adapted. One suitable way to accomplish this objective is schematically shown by Fig. 5 to which reference will first be made. In this form of grid winding mechanism the spool or drum (not shown) upon which the grid wire 11 is held is so supported that the wire from which the grid is to be formed, as it is unwound from the spool, passes through a guide hole or eye 15 in a guide block 17. The guide block is supported for slidable motion upon suitable guide rails (not shown for reasons of simplicity of illustration) in such a way that its path of motion with rotation of the lead screw or threaded shaft 19 is in the direction shown by the arrow adjacent to it. The guide block 17 has secured at its lower edge an internally threaded gripping section 21 which partially surround the threaded shaft or lead screw 19. This element is releasable from engagement with the spindle for rapid position to any point thereon, but when used to drive the block 17 by reason of rotation of the lead screw 19 the guide block 17 is adapted to move longitudinally thereof, as indicated by the arrow. The lead screw is suitably supported in end brackets (not shown) and arranged to be driven from any suitable source (also not shown) in order that its rotational rate may be caused to correspond to that of a suitable drum upon which the grid wires are adapted to be wound.

The drum upon which the wire is to wind to form the grid is conventionally represented at 23. It is carried by a support shaft 25 which extends parallel to lead screw 19 and which is spaced apart from the lead screw by a distance slightly more than the drum radius. The drum has its support shaft 25 suitably carried in bearing mem bers (not shown) at either end. There is a suitable drum drive arranged to move the drum, for instance, so that there is a 1:1 relationship of angular rotational speed of the drum and lead screw, although, of course, the peripheral speed of each component is different. I

The drum 23 preferably has a pair of slots 27 cut lengthwise thereof at diametrically opposite points. The slots are of a width conventionally represented as w and of a length which corresponds to the drum length. Usually two-slots are to be preferred, primarily due to drum size, but more may be used if desired. The wire 11 when drawn through the guide opening or eyelet 15 is caused to wrap around the drum as the drum rotates and tends to draw the wire in the direction shown by the arrow adjacent to it. The wire is so drawnonto the drum that when wrapped it forms a component which later will be installed in a cathode-raytube as an accelerating grid and focusing electrode, as above generally described.

It is known in the art that a grid element of this character is designed for positioning in proximity to the phosphor coated target of a cathode-ray tube in such a way as to control (with a suitable application of potential between the gridand the taget) the impact position ofa cathode-ray beam directed to the target through the grid. When the tube assembly, with which a grid-structure of the type herein described is to be used to recreate television images the tube target area is formed of strips of phosphors adapted to create luminous (electro-optical) image effects when a cathode-ray beam impinges thereon. Where these electro-optical effects are to represent an image in color and, illustratively, the resulting images are to be of the additive tricolor variety the phosphor coated target comprises a multiplicity of strips of coatings each of different characteristic as to formation and substance so that each produces light in one selected component color. Where tricolor operations are relied upon the phosphor strips, for instance, produce light individually in the colors red, green and blue. The individual phosphor strips are each approximately one-third the width of one point of the image to be recreated. The strips are arrange-d. cyclic sequence of the chosen color representation characteristics.

To achieve the results desired the phorphor strips may conveniently correspond in length to one dimension of the raster to be traced (for instance the height or'the width). The grid wires which are to be positioned adjacent to the phosphor coating on the tube target are arranged in the finally assembled tube in such a way that they are supported and positioned to extend in directions which are precisely parallel with one edge of the individual phosphor coated strips.

In the formation of the grid structure as herein to be explained the grid wires are initially supported in a location generally approximating that which they will have in a final tube. The grid wire 11 as unwound from the spool or reel (not shown) on which it has previously been wound is first fastened to a suitable holder on the rotating drum 23. Then, with rotation of the drum, the wire will wrap about the drum and the lower section of a grid wire holder or clamp bars, generally designated 33, to which further reference will be later made. At the moment suffice to say that the grid wire holder sections 31 are arranged so that two such elements fit within each slot 27 indicated as having the width w. The holder sections are held or wedged into the slots 27 in any desired manner, later to be discussed. The circumferential spacing along the periphery of the drum 23 between the slots is such that between each of the lower grid wire support elements 31 a length of grid wire 11 which is slightly in excess of that required for the finally installed grid may be wound. -With the drum 23 and the lead screws 19 being rotated and driven from any suitable source (not shown) at like speeds the grid wire if, as it unwraps from the spool or reel to wind upon the drum, winds along a series of turns representing a general spiral or helical path with the spacing between adjacent wires corresponding to the pitch of the lead screw 19 and which is approximately that desired for spacing between the grid wires in the finally assembled tube. The pitch, representing wire spacing in this instance, is a very close mechanical approximation to the final parallelly positioned wires although at this point in the operation the wires are not guided into the precision formed guide points.

To achieve a positioning of the Wires in the winding operation which will holdthem in a state from which they cannot readily move the wire is withdrawn or unwound from the reel or spool (not shown) against the force of a considerable drag sothat the wire, when wound, will, at

all times, be under reasonable tension. Also, by forming the outer surface 33 of each bracket support from. a material which tends to hold the wires tightly without slipping and yet which is sufficiently resilient that the thereby stripped wire is not damaged the operation can be rapid and yet reasonably precise. It has been found that a rubber strip or rubberized fabric which is of moderate softness, but which is not sufliciently soft to be cut by the tensioned wires, is suitable for this purpose.

It was above mentioned that the drum length should be approximately that of one raster dimension to be filled by the assembled grid wires with the other raster dimension being approximately the wire length as strung. If the wires are to run parallel to shorter dimension of the raster, of course, the drum height will be slightly in excess of the longer dimensions of the raster or if the wires are to run parallel to longer dimension of the raster then the drum height slightly exceeds the shorter dimension of the raster.

As the wire to form the grid is unwound from the storage spool and secured at approximately the outer periphery of the drum it can be seen that finally the wires will be wrapped substantially from one end of the drum to the other. The wire securement to one point on the drum or to one of the lower members prior to the start of the winding operation may, for instance, be done by slotting the member at two points and wrapping the wire over itself into the slot or the wire may be fastened over and about an anchor pin, or the securement may be in any desired manner which is suitable to the operation. The important point is that one end of the wire at the com mencement of wrapping operation should be anchored and from that point to the end of the winding operation the wires are located merely by engagement with the soft gripping surface 33 of the support bars.

With the winding operation completed, further provisions must be made for securing in a semi-permanent fashion the various wires in their wound position. To this end an upper gripping element or second clamp bar 35 having its under surface 37 formed to correspond to the surface 33 of the lower gripping element 31 is appropriately secured to the lower gripper by any suitable means, of which one is designated in Fig. 1. In this form of arrangement the upper gripping element 35' has a central slot 39 therein through which an appropriate fastening element, such as a bolt 41, is passed to thread into a threaded recess 43 in the lower member. The gripping clamps or supports 31 and 35 are each of rigid material and may be steel or any other substance strong enough to be fastened tightly without any substantial bending between the fastening points and sufficiently rigid to grip the wires wound on these supports between their lengths, it being borne in mind that the friction surfaces 33 and 37 prevent lateral slip in the wire.

At this point it may be mentioned that the lower gri ping members 31 may be formed in various ways but in order that the members may be removed readily from the drum slots 27 after being wrapped with the wires, one suitable form of construction is to provide a flattened edge surface 45 which is to contact with the edge of the drum slots 27. The upper surface of the gripping membsr against which the covering 33 is attached is also generally flat. The surface connecting the two flattened portions forms the gripping element in crosssection into a general sector shaped component 47, as indicated particularly by Fig. 7. The outer ends of the gripping memher which abut the end surface of the drum 23 are generally rectangular in cross-section but provide a shoulder portion 49 which contacts the ends of the drum and locates the gripping element longitudinally within the slot. So that the pairs of gripping eiements contained in each slot may be held tightly during the winding operation suitable provision is made for inserting a spreading shim between the rectangular shaped end elements to force the edges 45 tightly against the edges of the slot 27, or, in

another construction, the gripping members may be spread apart by a suitably arranged cam mechanism (not shown) of which many such types are known in the art.

After the grid wire has been wound, as explained, and the upper section 35 of the gripping elements has been securely fastened to the lower section 31 the spreading shims between the gripping members held in each slot may be removed. Concurrently, the .wires, now being tightly held in the wound position by the upper and lower elements 35 and 31 of the gripping or clamp member, may be cut apart along the line designated by dot-dash lines 51 and 51. This will then form about the periphery of the drum two grid wire sections. With the grid wire support elements now being less tightly fitted into the drum slots and the surface 47 of the gripping elements being of arcuate contour it can be appreciated that by mereiy rolling the gripping members about the upper edge of the drum slot as a fulcrum the gripped wires may be removed from the drum surface. So removed the wires are formed into sets, the wires of each set being spaced substantially equidistant one from the other and each securely anchored at each end into the clamp blocks or grid wire supports 31 and 35. The length of the wires thus assembled exceeds slightly the length desired for the grid. The spacing of the wires closely approximates that desired for the final grid. Accordingly, at this point, provision can be made assembling the so formed loosely mounted grid wires into a final grid structure in which the wires will be located with great precision and wherein the wires will be held under the proper tension with respect to the wire supporting form to which it is fastened.

Assuming now that the grid has been preliminarily formed by some procedure such as that illustratively described above, the grid wires 11, when thus positioned approximately in the relationship in which they are finally to be supported, are positioned to rest in a plane to be parallel to the plane of a bed plate or support 63. One of the sets of support clamp bars 31, 35 is supported upon the bed plate 63 by the shoulder end sections 49 and fitted between a pair of locating blocks 65 and 67. These blocks may be fixed or one may be fixed and the other moved in and out (and in a direction corresponding to the wire length) relative to it in much the same manner as the jaws of a vise are movable relative to each other so as to be clamped securely. This construction is illustrated only by diagram for reasons of simplicity of show- Substantially adjacent to the clamp bars 31 and 35 there is positioned a component herein termed a precision positioning locating bar 69, which is shown in more detail in Figs. 3 and 4. The bar 69 has V-shaped recesses 71 spaced from each other with great precision and very accurately cut in both spacing and depth. With the grid wires 11 held by the clamping bars and with a sufficient number of grid wires assembled the individual wires of the grid may then be located in the recesses 71 of the precision positioning bar. So locating the wires in the notches or recesses 71 of the precision positioning bar 69 provides an initial approximation to the precise optimum on correct wire positioning at one end. There is also supported at the opposite end of the bed plate 63 a second precision cut grid wire positioning bar 69 of a character precisely like that of the positioning bar 69. These bars are held securely to the bed plate support 63 so that their location relative to it is permanently fixed. There is also mounted upon the bed plate or support 63 a pair of frame locating supports 71 and 71' upon which the grid wire support frame 75 is adapted to be positioned, with the ends of the support frame 75 upwardly turned as shown at 77 and with the bottoms of the notches 71 in the prepositioning bars 69 located at a distance from the top of the upturned ends 77 of the support frame 75 which is rigidly controlled. While various distances may be used it has been found in practice that a particularly useful construction is one where the wires 11 (prior to final anchoring) are held at about 0.030" above the top of the upturned frame ends 77. To insure this precise positioning the individual wires 11 of the grid are located in the slots 71 of the positioning bars 69 and 69'. With one of the clamp sets 31 and 35 arranged to rest upon the base or bed plate 63 and secured thereto at least temporarily the other set of clamps 31', 35' which holds the opposite ends of the wires 11 may then be either spring loaded with respect to its positioning relative to the clamp bars 31 and 35 or the tightened clamp bars 31 and 35' may be arranged to overhang the end of the base or bed plate 63 and be sufliciently heavy as to place the wires 11 when located in the notches of the positioning bars under considerable tension.

The wires 11, when so drawn taut and held in fixed position relative to the upturned edges 77 of the support frame 75 are next to be secured and permanently fastened. At this point it is worth again mentioning that the positioning bars 69 and 69' are fabricated with great precision to insure accuracy in both the spacing and depth of the grid-wire locating slots 71, so that all grid wires when pressed into the slots and tightly stretched will align themselves in coplanar fashion and with precisely the spacing of the slots. At the same time all wires will be held in an accurately fixed position relative to the grid wire support frame.

It may be worth mentioning that the support frame 75 has a central window area the size of which is of the same order as that of the raster area to be traced by the scanning cathode-ray beam developed in well known manner by an electron gun within the tube in which the grid structure is to be assembled. In most instances, the window area of the frame is of generally parallelogram shape and it will be so described in connection with an illustration of the invention. However, it is to be understood that the invention is in no sense limited to such a shape supporting frame by reason of the principles herein explained.

For most uses of the tube the grid wires are required to perform not only an accelerating and focusing function (in conjunction with the conductively coated tube target element) but also a deflection action, as above mentioned, whereby the final impacting cathode-ray beam is adapted to be shifted from its undeflected point of impact within a region bearing a fractional relationship to the spot area or width to which the impacting beam should be directed to the target. Under such conditions, since the frame itself is formed of material which is conducting and it is essential that adjacent wires of the grid structure be insulated one from another, the fastening of the grid wires is provided by insulating elements. For this purpose the upturned ends 77 of the conducting frame 75 are spaced from the grid wires 11 by the distance desired for insulation and the frame is then coated along its edges with a form of insulating covering into which the grid wires may be embedded and secured.

One suitable fastening contact is provided by way of an insulating material which will bond to or hold to both the grid wires and the supporting member. One such form of bond is in the form of a cement known as Sauereisen Insa-lute No. 1 Cement which is adjusted to match the expansion of the type of stainless steel grid wire and the material of the grid frame.

The Sauereisen cement is represented at 83 in Fig. l and it will be seen to extend upwardly from the top of the upturned edges 77 of the grid support frame 75. While the cement is in its generally plastic state it is built up to surround the grid wires 11 while they are held in a taut state. The complete bed plate, clamped wires and, in fact the complete assembly, is then placed in a baking oven wherein the assembly is baked to drive out the moisture from the cement and thereby to cause the cement to harden. The baking period is usually about four (4) hours with the baking at about 250 F., although this is purely illustrative and may be varied as circumstances and conditions permit.

For schematic representation of a form of tube device with which the invention herein set forth and claimed may be used, reference may be had to the schematic showings of Figs. 8 and 9. In considering these showings it should be appreciated that the schematic representation is for the purpose of setting forth a functional relationship rather than to present any showing which is intended to be according to scale or to represent actual size relationship of any of the components with respect to each other. Illustratively, the grid components shown in Fig. 9 indicate by a relatively few of the number of wires actually constituting the grid, although the functional relationship of the positioning of these wires relative to the target is apparent.

In Figs. 8 and 9 a portion of the tube envelope of the cathode-ray tube, that is the generally conical-shaped bulb portion, has been represented at 85. It will be understood, of course, that the cathode-ray tube envelope also comprises a neck portion (not shown) which, in known fashion, would be located to the left of the broken line of Fig. 8 and which would include the usual electron gun comprising the means to produce and develop the beam of'cathode rays which is directed toward the final target to be impacted. The impacted target area is visible to a looker through the transparent endwall 87 of the tube although the target actually impacted is represented here schematically by the base or target member 89.

It will be appreciated that the grid wire support frame comprising the end member 75 to which the grid condoctors are secured and the spacing side member 76 is adapted to rest upon this target element $9 in such a position that the upturned ends 77 and 77 extend outwardly from the target in the direction toward which the beam of cathode rays is developed. The grid wires 11, which are strung and supported relative to the end member of this frame in the manner described particularly in conjunction with the showings of Figs. 1, 2 and 3, are held in the desired location relative to the upturned ends 77 and 77 by the Sauereisen cement shown at 83. The window area formed between the frame end and side members 75 and 76 is thus spanned by the wires 11 of the grid.

Thus, the representation is purely schematic and for clarification purposes in Fig. 9 the attachment means for frame 75 is shown at the end portion only as its resting on the target plate 89. The side or lateral edges 76 to form the rigid construction similarly rest on the target plate 89.

When the grid wires 11 are secured to the frame 75 they are connected alternately to header connections schematically represented at 91 and 93, so that alternate wires of the grid are electrically connected. The grid wires of the tube sets thus formed and which thus are interleaved with respect to each other are then connected to external circuits by way of a connection passing out of the tube preferably through a seal 94 in the wall of the tube with the contactor being by way of the connection shown at 95 for connecting to the header 91 and at 96 for connecting to the header 93.

Purely in a schematic form of illustration, the target plate 89 is shown in Fig. 9 as supported from the tube wall by laterally extending brackets 97 and 98 suitably secured and attached at one end to the target plate and at the other end to the tube wall. These brackets may be either metal or vitreous material, either of which may be secured in well known fashion to the vitreous target element 89 and to the tube shell or cone 85, which shell may be either metal or a vitreous material as desired and in accordance with tube practice. It has.

10 alreadybeen explained herein and is well known from the art that the strung grid wires are arranged to extend in directions generally parallel to phosphor strip coatings (not shown) carried upon the target plate and adapted to face that side of the target plate toward the grid. Under operating conditions such that a control of the relative potential of the grid wires with respect to a metallic film (not shown) coating that side of the target plate toward the grid and resting upon the phosphor will be determined the degree of convergence or focusing of the electron beam of the tube gun projected through theagrid wires .11 toreach the target surface 89. Like- 'wise, a control of the potential of adjacent grid wires a to the target, not;only can be focused between the grid and the target plate, but also can be controlled as to the precise point of impact'through the introduction of .rnicrodeflections thereupon by the application of suitable potentials to the grid wires.

At this point it is emphasized that the baking opera- .tion which-resultsin the grid wires being bonded to the frame by means, of the insulating cement is not the same baking operation as in the final processing and sealingoff of the tubeasisfinallytprepared. The baking operation in which the cement is caused to harden is at the indicated low'temperature at which the gripping surface of the semi-permanent gripping elements 31, 35 will not be damaged and yet the moisture will be driven from the cement to cause itto harden. The semi-permanent gripping components which might'be damaged by high temperature are, of course, removed from the grid structure prior to assembling the final gridwithin the tube for the final tube bake-out.

In another form of construction, a fastening glass may be used. So formed, the frame may have its upturned edges, relative to which the wiresll are-to be permanently secured, formed of glass, such as Corning Type G-12. For fastening the grid wires under such conditions to the support frame a glass cane is laid on the support frame and the frame and the glass together are brought up to sealing temperature, and while the glass is plastic the wires 11 of the grid are then pressed into 'the glass. Upon cooling, the glass contracts around the wires and holds them securely in place. Sincethe diametervof'the wire is extremely small (usually about 0.003 to 0.005") the total mis-match of expansion of the glass and the wires is small and consequently'no substantial problems are presented.

For some forms of tubes, as above stated, all of the grid wires may be held and operated at the same potential. Under such circumstances the upturned ends 77 of the grid wire support frame 75 may conductively contact the Wires 11, in which case the attachment of the grid wires 11 to the frame then may be accomplished by welding, hard soldering-brazing, or establishing a suitable metal-to-metal contact by well known techniques while the wires are stretched relative to the support frame. In such a use of. the grid structure, the grid mechanism would function as a focusing component and also, in conjunction with .the coated end of the tube as a conductor, in the capacity of a portion of an accelerating electrode assembly. It is apparent that the metal-to-metal fastening should be such that the weld, soldering or brazing must be accomplished while the wires are stretched tightly across the edge of the support frame. In the case of the direct metal-to-metal contact the support frame may contact the wires directly and the 0.030" spacing (or some other appropriate value) is unnecessary.

It is one of the important features of this invention to so form the grid wires and the support frame that the arrangement as a whole will Withstand the bake-out temperatures encountered in the tube manufacture. As

was pointed out above it is possible to establish to a very high degree of precision the absolute coefficient of linear expansion of any ferrous alloy with a rigorous control of the addition of nickel thereto maintained. In one form of construction the grid wires may be of a type which is known as Type 302 stainless steel wires which then may be attached (through the Sauereisen cement) to a frame of a type known as Type 430 stainless steel. Under such circumstances the grid wires themselves will have a higher coeflicient of linear expansion than the frame so that as the heating occurs within the frame during bake-out, the grid wires will expand to a degree greater than the frame with the result that in the bakeout procedure the grid wires sag relative to the frame and they are not placed under tension by reason of the frame expansion. With cooling following bake-out the contraction of the grid wires relative to the frame is such that the desired tension is placed in the wire after the seal has been established. By carefully choosing the relative expansion characteristics of the frame and the wires the desired tensioning is automatically established.

In an example where the glass is used to bond the wires to the frame it may be noted that Corning Type G-12 glass may be bonded to Type No. 446 stainless steel, for instance, or to a special modified Type 430 stainless steel by the application of heat in a manner similar to that used for sealing face plates to the metal shells for television tubes.

In the case where the grid wires are to be used in a tube in such fashion that deflection is to be accomplished by the grid as well as focusing and acceleration alternate wires of the grid are bent downwardly and upwardly and attached to a common conductor external to the frame 75 with the conductors suitably secured within the tube in a manner not shown which is adequate to hold the separate sets of Wires out of electrical contact one with the other. This feature of invention is shown illustratively by an application of James T. Vale, Serial No. 252,664, filed October 23, 1951, and is also shown by an application of Robert Dressler entitled Cathode Ray Tube Accelerating Structure assigned to the same assignee as this application. In cases where grid wires are all adapted to be maintained at the same potential any suitable arrangement for bringing about an electrical connection from a source external to the tube and the wires may be utilized, and such per se forms no part of the present invention.

From what has been stated above it will be apparent that this invention provides for precisely establishing the spaced relationship of the grid wires with respect to each other by a mechanism external to the tube, such as precision positioning bars 69. The so-positioned grid wires are next stretched between the precision positioning bars. While the wires are held in such a stressed or taut state they are permanently secured to a framework which then is held securely adjacent to the so-supported wires. When the wires are attached thereto, the percision and accuracy of positioning by the aid of mechanisms separate from the tube components themselves is maintained in the fastened wires forming the final grid structure. Under such circumstances the necessary precision of operation is brought into the tube by means of a single mechanism usable for all tubes manufactured rather than to provide or require any high degree of precision in the fabrication of the grid frame component to be used within the finally assembled tube. Under the circumstances faster and more efiicient manufacturing processes can be expected with reduced labor costs as well as reduced shrinkage in manufacture due to imperfect formation of the grid structure to be produced. Many and various modifications of the invention, of course, can be realized from what has been set forth in this disclosure.

From what has been said above, it will become apparent that in' practicing of the foregoing method of forming the grid structure other forms of structures for semi-permanently assembling the grid may be adapted prior to the final operation. In another form of the invention, a multiplicity of tension-type de-reeling spools upon which the grid wire has been Wound are supported plicity of aligned wire passing openings each of approximately the diameter of that of the wire. The wire, drawn from the spools, is pulled through these openings. Each opening is' spaced along a line from the opening on either side thereof by a distance center-to-center which is approximately that desired for the center-to-center grid wire spacing in the finally assembled grid structure for mounting in the tube envelope. In this modification, the wires are drawn from the spools which in some re- 'spects resemble the operation used to draw threads from numerous spools in Weaving cloth. The number of openings in the pre-positioning bar correspond, of course, to the number of wire strands to be drawn to form the grid and likewise to the number of spools from which the grid wire is to be withdrawn. The wire from the spools is then threaded through the openings in the pre-positioning bar to provide protruding therefrom a number of strands corresponding to that of the final grid to be assembled. In this form a pair of positioning or clamping bars corresponding, for instance, to those shown at 31 and 35 (see Figs. 5 through 7) and each having a wire gripping surface generally like that shown at 33 and 37 is securely clamped on either side of the wires to hold them in substantially the same spaced relationship as that in which they protrude through the openings in the pre-positioning bar. The so-clamped wires are then pulled to draw wire from the spool or reel through the openings in the positioning bar and to provide extending therefrom to the positioning bar a length of wire which is approxmately that length desired for the grid. At this time a second set of clamping bars, like those shown at 31 and 35, is clamped about the wires protruding through the openings in the pre-positioning bar to form thereby between the two sets of clamps a plurality of wire strands spaced from each other at the semi-permanent anchoring points in the clamp by approximately the final desired spacing.

To form the final grid structure, the so-clamped wires are then drawn slightly further through the pre-positioning bar and a third clamp pair is positioned close to the described second clamp pair and between the second pair and the pre-positioning bar. The series of wires extending the short distance between the second and third pairs of clamping bars is then severed and there is providedbetween the first two pairs of clamping bars a grid structure which is approximately like that assembled with Fig. .1. The clamped wires which protrude through the openings of the pre-positioning bar at this time can then be. considered as held by the third clamp pair and by means of which they may be drawn from the multiplicity of spools to provide a complete new group of wires for the next grid, and so on.

In. this form of the operation, it will be observed that each individual grid wire is drawn from a separate spool. In the operation described illustratively by Fig. 5 the separate grid wires are all drawn from a single spool. Either method is suitable to form the final grid. The broad proposition of forming the final grid is essentially practiced by either form of the operation. The important and significant feature is that the plurality of grid wires is initially assembled with the wires semi-permanently clamped in approximately the desired final spacing. Upon being so assembled, the wires are then supported in such relationship to the precise or optimum positioning bars, such as 69 and 69, that each wire can be precisely located in the slots 71 and spaced from each adjacent wire by the exact spacing desired. The precise manner of initially clamping the Wires in the semi-permanent clamps is thus a matter of choice, and either proposal will suffice to provide the final end result.

In the description which has so far been set forth the tube to be built is described as one in which the grid wires are each equally spaced from the other. Such construction is actually simpler to make and to align than many others, but it is, nonetheless, to be understood from what has herein been set forth that the principles of the invention herein enumerated are applicable to other forms of tube construction. As an example, in some tubes (and particularly the large size tubes) it may be desirable that the spacing of the grid wires relative to each other he changed toward the outer edges of the final raster area. This is due, for instance, to the fact that as the angle through which the scanning cathoderay beam is deflected increases to an extreme deflection from a more or less central portion the subtended beam sweep path projected upon a planar surface for any given deflection becomes greater and greater with increasing angle. Also, and especially in connection with tubes wherein the end wall on which the phosphor coating is placed is of a curved characteristic, it frequently becomes desirable in order that there shall be :a minimum of distortion in the finally developed image to have the grid wires at unequal separation from the plane of the tube target. To achieve this result it will be apparent that the depth of the locating slots in the precision positioning bar may be progressively different throughout its length. In this case the wires will not all be coplanar but, even so, the principles of the invention can still be achieved. Also, there may be a combination of such arrangements. The invention consequently, is intended to set forth a broad principle and the form in which it has been illustrated is an example of one of its preferred and illustrative forms.

Having now described the invention, what is claimed 18:

1. A grid electrode structure for assembly into a cathode-ray tube comprising a metal frame having its edges define a central window area, a plurality of metal grid wires strung between the edges of the frame, said grid wires having a coeflicient of linear expansion which is higher than that of the frame so that with heating during tube bake-out the frame and the wires expand to different degrees, means to anchor the wires permanently to the frame edges in insulated relationship to each other, and means to establish electrical connection to the wires.

2. A grid structure for cathode-ray tubes comprising a metal frame having a central window area of generally parallelogram configuration, a plurality of metal grid wires having a coefficient of linear expansion which is greater than that of the frame strung parallelly substantially equally spaced from each other and in substantially coplanar relationship between the support edges of the frame and across the window areas, the greater coefiicient of linear expansion of the wires permitting the wires to expand to a greater degree than the frame during tube bake-out and subsequently to return to a taut state across the window area, an insulating cement carried upon the edges of the frame over which the wires pass and in adhering relationship to each of the frame and the wires to hold the wires individually insulated from each other and from the support frame, and means to establish electrical connection to the wires.

3. The grid structure claimed in claim 2 comprising, in addition, means to connect alternate wires of the grid electrically together external to the window area so that the electrical connection to the wires permits of application of different potentials to adjacent grid wires.

4. A grid electrode structure for cathode-ray tubes comprising a metal frame having a central window area, a plurality of conducting metal grid wires having a coefficient of linear expansion which is higher than that of the frame strung parallelly between the support edges of the frame and across the window area, the diiferent coefficients of linear expansion permitting the wires to expand to a greater degree than the frame during tube bake-out, an insulating cement carried upon the edges of the frame in adhering relationship thereto and surrounding the conductors and tightly bonding the grid wires and the support frame in insulating relationship to each other, and means to connect electrically alternate wires of the grid to provide two sets of electrically connected wires.

5. A grid electrode structure for cathode-ray tubes comprising a metal frame having a central window area, a plurality of conducting metal grid Wires parallelly and tightly stretched across the window area and between the edges of the frame, the spacing between the wires being of the order of the width of a point in an image to be resolved by the tube, the said grid wires having a coeflicient of linear expansion which is higher than that of the metal frame, means for attaching the wires to the edges of the frame in insulating relationship thereto and insulated from each other, means to connect electrically alternate wires of the grid to provide two sets of electrically connected wires, and means to establish electrical contact to the wires.

6. A grid structure adapted for inclusion in a cathoderay tube in a region closely adjacent to the phosphorcoated target of the tube comprising a metal frame having a generally parallelogram-shaped central open area of configuration approximating that of a raster to be defined by scansion within the cathode ray tube when assembled, said metal frame having one selected coefiicient of linear expansion, a plurality of metal grid wires each of a wire diameter representing a minor fraction only of the diameter of one image point of an image to be recreated within the traced raster area, said wires being strung between opposed edges of the parallelogram-shaped metal frame in parallel relationship one with respect to the other and separated one from the other by distances approximately equal to one dimension of a picture point to be traced within the raster, said wires having a coeflicient of linear expansion which is higher from that of the frame, means for anchoring the wires to the frame and insulating the wires individually with respect to each other and with respect to the supporting frame, and means for connecting alternate wires electrically external to the frame window to form the wires into two sets electrically separated from each other.

References Cited in the file of this patent UNITED STATES PATENTS 1,934,097 Simon Nov. 7, 1933 2,182,968 Lunsford Dec. 12, 1939 2,194,551 Holman Mar. 26, 1940 2,282,392 Bieling May 12, 1942 2,397,233 Bingley Mar. 26, 1946 2,446,791 Schroeder Aug. 10, 1948 2,463,535 Hecht Mar. 8, 1949 2,530,538 Rack Nov. 21, 1950 2,653,263 Lawrence Sept. 22, 1953 2,683,833 Zaphiropoulos July 13, 1954 2,695,372 Lawrence Nov. 23, 1954 FOREIGN PATENTS 124,909 Australia July 31, 1947 600,257 Great Britain Aug. 5, 1948 

